/*******************************************************************************
 * Copyright (c) 2000, 2007 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.elwiki.preferences.ui.registry;

import java.util.Arrays;

import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.core.runtime.IExtension;
import org.eclipse.core.runtime.IExtensionPoint;
import org.eclipse.core.runtime.IExtensionRegistry;

/**
 * Template implementation of a registry reader that creates objects representing registry contents.
 * Typically, an extension contains one element, but this reader handles multiple elements per
 * extension.
 *
 * To start reading the extensions from the registry for an extension point, call the method
 * <code>readRegistry</code>.
 *
 * To read children of an IConfigurationElement, call the method <code>readElementChildren</code>
 * from your implementation of the method <code>readElement</code>, as it will not be done by
 * default.
 */
public abstract class RegistryReader {

	// for dynamic UI - remove this cache to avoid inconsistency
	// protected static Hashtable extensionPoints = new Hashtable();
	/**
	 * The constructor.
	 */
	protected RegistryReader() {
	}

	/**
	 * Logs the error in the workbench log using the provided text and the information in the
	 * configuration element.
	 */
	protected static void logError(IConfigurationElement element, String text) {
		IExtension extension = element.getDeclaringExtension();
		StringBuffer buf = new StringBuffer();
		buf.append(
				"Plugin " + extension.getNamespace() + ", extension " + extension.getExtensionPointUniqueIdentifier());//$NON-NLS-2$//$NON-NLS-1$
		// look for an ID if available - this should help debugging
		String id = element.getAttribute("id"); //$NON-NLS-1$
		if (id != null) {
			buf.append(", id "); //$NON-NLS-1$
			buf.append(id);
		}
		buf.append(": " + text);//$NON-NLS-1$
		// TODO: :FVK: WorkbenchPlugin.log(buf.toString());
	}

	/**
	 * Logs a very common registry error when a required attribute is missing.
	 */
	protected static void logMissingAttribute(IConfigurationElement element, String attributeName) {
		logError(element, "Required attribute '" + attributeName + "' not defined");//$NON-NLS-2$//$NON-NLS-1$
	}

	/**
	 * Logs a very common registry error when a required child is missing.
	 */
	protected static void logMissingElement(IConfigurationElement element, String elementName) {
		logError(element, "Required sub element '" + elementName + "' not defined");//$NON-NLS-2$//$NON-NLS-1$
	}

	/**
	 * Logs a registry error when the configuration element is unknown.
	 */
	protected static void logUnknownElement(IConfigurationElement element) {
		logError(element, "Unknown extension tag found: " + element.getName());//$NON-NLS-1$
	}

	/**
	 * Apply a reproducable order to the list of extensions provided, such that the order will not
	 * change as extensions are added or removed.
	 * 
	 * @param extensions the extensions to order
	 * @return ordered extensions
	 */
	public static IExtension[] orderExtensions(IExtension[] extensions) {
		// By default, the order is based on plugin id sorted in ascending order.
		// The order for a plugin providing more than one extension
		// for an extension point is dependent in the order listed in the XML file.
		IExtension[] sortedExtension = new IExtension[extensions.length];
		System.arraycopy(extensions, 0, sortedExtension, 0, extensions.length);
		Arrays.sort(sortedExtension, (arg1, arg2) -> {
			String s1 = ((IExtension) arg1).getNamespaceIdentifier();
			String s2 = ((IExtension) arg2).getNamespaceIdentifier();
			return s1.compareToIgnoreCase(s2);
		});
		return sortedExtension;
	}

	/**
	 * Implement this method to read element's attributes. If children should also be read, then
	 * implementor is responsible for calling <code>readElementChildren</code>. Implementor is also
	 * responsible for logging missing attributes.
	 *
	 * @return true if element was recognized, false if not.
	 */
	protected abstract boolean readElement(IConfigurationElement element);

	/**
	 * Read the element's children. This is called by the subclass' readElement method when it wants to
	 * read the children of the element.
	 */
	protected void readElementChildren(IConfigurationElement element) {
		readElements(element.getChildren());
	}

	/**
	 * Read each element one at a time by calling the subclass implementation of
	 * <code>readElement</code>.
	 *
	 * Logs an error if the element was not recognized.
	 */
	protected void readElements(IConfigurationElement[] elements) {
		for (int i = 0; i < elements.length; i++) {
			if (!readElement(elements[i])) {
				logUnknownElement(elements[i]);
			}
		}
	}

	/**
	 * Read one extension by looping through its configuration elements.
	 */
	protected void readExtension(IExtension extension) {
		readElements(extension.getConfigurationElements());
	}

	/**
	 * Start the registry reading process using the supplied plugin ID and extension point.
	 * 
	 * @param registry       the registry to read from
	 * @param pluginId       the plugin id of the extenion point
	 * @param extensionPoint the extension point id
	 */
	public void readRegistry(IExtensionRegistry registry, String pluginId, String extensionPoint) {
		IExtensionPoint point = registry.getExtensionPoint(pluginId, extensionPoint);
		if (point == null) {
			return;
		}
		IExtension[] extensions = point.getExtensions();
		extensions = orderExtensions(extensions);
		for (int i = 0; i < extensions.length; i++) {
			readExtension(extensions[i]);
		}
	}

	/**
	 * Utility for extracting the description child of an element.
	 * 
	 * @param configElement the element
	 * @return the description
	 */
	public static String getDescription(IConfigurationElement configElement) {
		IConfigurationElement[] children = configElement.getChildren(IWikiRegistryConstants.TAG_DESCRIPTION);
		if (children.length >= 1) {
			return children[0].getValue();
		}
		return "";//$NON-NLS-1$
	}

	/**
	 * Utility for extracting the value of a class attribute or a nested class element that follows the
	 * pattern set forth by {@link org.eclipse.core.runtime.IExecutableExtension}.
	 * 
	 * @param configElement      the element
	 * @param classAttributeName the name of the class attribute to check
	 * @return the value of the attribute or nested class element
	 */
	public static String getClassValue(IConfigurationElement configElement, String classAttributeName) {
		String className = configElement.getAttribute(classAttributeName);
		if (className != null) {
			return className;
		}
		IConfigurationElement[] candidateChildren = configElement.getChildren(classAttributeName);
		if (candidateChildren.length == 0) {
			return null;
		}

		return candidateChildren[0].getAttribute(IWikiRegistryConstants.ATT_CLASS);
	}
}
